Control for absorption refrigerating systems



March 10, 1942. F. P. SHANNON CONTROL FOR ABSORPTION REFRIGERATINGSYSTEMS Filed May 22, 1941 2 Sheets-Sheet 1 FRANCJ S P. fiHANNQNINVENTOR ATTORNEY March 10, 1942. P. SHA NON I 2,275,997

CONTROL FOR ABSORPTION REFRI'GERATING SYSTEMS Filed May 22, 194i 2Sheets-Sheet 2 v P a J- I ll m g Q i 2 f (0 K i m i. j

\9 .9 I a L N A 3 x 0 a i ll l lll el r uau} -5 FRANCIS P. SHANNON I 8INVENTOR 5 BY MAW ATTORN EY Patented Mar. 10, 1942 CONTROL FORABSORPTION REFRIGERAT- v I'NG SYSTEMS Francis P. Shannon, Louisville,Ky., assignor to Henry Vogt Machine Company, Louisville, Ky., acorporation of Kentucky Application May 22, 1941, Serial No. 394,680

4 Claims. This invention relates to control systems for absorptionrefrigerating systems of the closed cycle type wherein weak liquor froma heat exchanger and gas from an evaporator are both fed to the absorberto form a'strong liquor.

In absorption refrigerating systems of this type, the flow of weakliquor preferably should remain constant for any given d condition.Since it tends to vary, a flow control valve is usually in- In onecontrol system wherein the flow control valve is held indifferentpositions by difierent operating air pressures, an air-leakage relay,re-

sponsive to changes in the weak liquor flow, is used to change theoperating air pressure in order to move the valve'and thus restore theflow, While a reset mechanism, responsive to changes in the operatingair pressure, is employed to reset the air-leakage relay so that, whenthe flow is restored, the relay will maintain the air pressure at thechanged value. With a straight flow control of this character, it isnecessary "manually to adjust the connection between the reset mechanismand the air-leakage relay from one control point to another toaccommodate changes in either the capacity of the system or in theoperating ratio of the weak-liquor flow to the flow of gas to theabsorber. In another control system of this same general type, theair-leakage relay is made responsive to changes in a predetermined ratiobetween the weak-liquor flow and the flow of gas to the absorber inorder to change the operating air pressure and thus restore the ratio,the reset mechanism operating as before so that when the ratio isrestored, the air-leakage relay will operate to maintain the airpressure at the changed value. While thi arrangement automaticallyaccommodates changes in capacity, it remains necessary manually toadjust it from one control point to another to accommodate necessarychanges in ratio.

The principal object of the present invention is to provide an entirelyautomatic control system of this same general type wherein theconnection between the reset mechanism and the ratio.

air-leakage relay is changed automatically from one control point toanother to accommodate changes in either the capacity or the operatingAnother object is to providein combination with a flow control anauxiliary control for automatically adjusting the connection between thereset mechanism and the air relay mechanism of the flow control asconditions require.

The invention is illustrated in the accompanying drawings, wherein:

Figure l is a schematic view of one embodiment of my invention; and

Figures 2, 3 and 4 are schematic views showing the relative positions ofvarious parts of airbefore, during and after a resetting operation.

The drawings conventionally illustrate an absorber and a fixed meteringorifice l forming a part of a conventional flow indicator.

The flow indicator registers the pressure drop across the meteringorificel by means of a mercury manometer 8 having on one side a float 9which is connected, through appropriate linkage, to a flow indicatingarm It). With this arrangement, it will be evident that the indicatingarm it will swing about its upper end pivot in response to variations inthe flow of weak-liquor and that it will always occupy one predeterminedangular position for one given flow and another predetermined angularposition for another given flow. With the absorption system operating ata given capacity, the movement of the flow-indicating arm I 0 from thegiven flow position for that capacity initiates the correcting operationof the weak-liquor valve 5 through an intermediate control mechanism F.

While any suitable control mechanism ,F may be employed, a mechanism ofthe type schematically illustrated is preferred. This particular type ofmechanism is presently manufactured by the Foxboro Company of Foxboro,Massachusetts. and marketed as Model 10 Stabilog with M/20 StabilsetHydronflf The air relay R comprises a flapper l2 and a follower l3 bothmounted for pivotal movement on the asme axis. The flow-indicating armIII .the reset mechanism M is mechanically connected through link H tothe flapper I2 to impart to the flapper whatever movement it undergoes.The flapper l2 thus initiates the operation of the control mechanism Fin response to flow variations. The follower I3 is in the form of an airnozzle mounted adjacent the flapper I2 for pivotal movement through thesame range of predetermined angular positions but normally is held inone predetermined angular position by the reset mechanism M to which itis mechanically connected.

The reset mechanism M comprises a ingbellows I4 having end bar l5 andits inner end separated by a common equalizer bar Hi from a slow-actingbellows ll. These parts are interposed between an upper spring I8 and alower fixed framework IS with the outer end of the fast-acting bellowsl4 operating against spring l8 and the corresponding end of theslow-acting bellows l1 secured to the fixed framework IS. The resetmechanism is mechanically connected to the folfast-actits outer endclosed by an lower l3 of the air relay R through a floating bell crank20, this connection including: link l3a connecting the follower [3 toone end of the bell crank 20; link a. connecting the end bar Hi to thefloating pivot of the bell crank and link I60. connecting the common barIE to the other end of the bell crank.

Air under pressure is supplied to the control system from some suitablesource such as the supply tank 22. This tank is connected through thepressure chamber of a control head 23,

capillary coil 24 and line 25 to both the nozzle l3 of relay R and adiaphragm 26, the latter being at the terminus of line 25. The diaphragm26 is mechanically connected to a control valve 21 in the valve chamberof the control head 23. The valve chamber has open communication withthe weak liquor valve 5 through a terminal pressure line 28. It also hasopen communication with the air lines leading to both bellows of but, inthis connection, it will be noted that the line leading to the fastacting bellows I4 is unobstructed while the line leading to theslow-acting bellows l'l contains a capillary coil 29.

The valve chamber of the control head 23 is also connected, through oneoriflce, to receive air from the pressure chamber of the control headand, through another orifice, to discharge air to atmosphere, theseorifices being controlled'by the valve 21. In the central position ofthe valve 21, air enters the valve chamber from the pressure chamber andescapes from the valve chamber into outside atmosphere at rates whichmaintain what may be termed a medium operating air pressure in theterminal pressure line 28 and in the lines' leading to the resetmechanism M. 'As the valve 2'l'moves progressively left-ward theoperating air pressure is progressively reduced because the rate atwhich air enters the chamber is progressively reduced while the rate atwhich it escapes from the chamber is increased. On the other hand, asthe valve 21 moves progressively rightward, the operating air pressureis progressively increased because rate at which air enters the chamberis increased while the rate at which it escapes from the chamber isreduced.

In describing the operation, it is assumed that a desired weak-liquorflow of 100 pounds per minute is established with the flapper l2 at the100-pound position, the air nozzle I3, the end bar 15 and the common barHi, all at positions Now, if the weak-liquor flow drops from pounds to,say 98, the flapper will swing counterclockwise to the 98-pound positionas indicated in Figure 3. This increases the air leakage from relay R,and proportionately deflates diaphragm 26 which pulls valve 21rightward. Such movement of valve 21 increases its air-entry port anddecreases its air-escaping port, causing the operating air pressure toincrease to a higher value. The increase in operating air pressurecorre- 'spondingly opens the weak-liquor valve 5, permitting theweak-liquor flow to increase to 100 pounds. As a matter of fact, theincrease in flow will usually go above 100 pounds but, for the sake ofclarity in describing the operation of the control, a return to l00pounds will be assumed. As the weak-liquor flow returns to 100, theflapper 12 returns from the 98-pound position to its original 100-poundposition.

Since a larger opening of valve 5 is now required to maintain a100-pound flow, a correspondingly larger operating air pressure must bemaintained. To maintain a larger air pressure, the air leakage relay Rmust. be reset to provide a larger rate of air leakage, one sufficienttohold diaphragm 26 under whatever smaller pressure is necessary tosecure the higher operating. air pressure. The reset mechanism Mfunctions to reset the air leakage relay Rto the new rate of airleakage.

Figure 2 schematically illustrates the relative positions of the variousparts in the air-leakage relay R and the reset mechanism M before theflow deviation occurred. Referringto this flgure, it will be noted thatthe flapper I2 is at the 100-pound position, while the nozzle I3, endbar 15 and common bar l6 are all at positions numbered 10. When the flowdeviatesfrom 100 pounds to 98, and the operating air pressure increases,the reset mechanism M is subject to the increased operating pressure.Due, however, to the capillary 'coil 29, the increase in operating airpressure is reflected more rapidly in the fast-acting bellows l4 than itis in the slow-acting bellows l1. Consequently, the fast-acting bellowsl4 expands rapidly, pushing end bar [5 upwardly to position, say, #12,and common bar 16 downwardly to position, say, #9, as indicated inFigure 3. These movements of the bars I5 and I6 are transmitted to thefollower iii of the air relay R, adjusting the follower to a newpositionapproximating the final position necessary to maintain thehigher operating pressure.

As the. slow-acting bellows I'I expands, it pushes the common bar l6upwardly from position 9 in Figure 3, thus effecting, through link lia,a further adjustment in the position of the follower 13. Since each ofthese adjustments has some effect upon the air-leakage rate, and sincethe air leakage rate determines the operating air pressure,eachadjustment is necessarily accompanied by a change in the operatingpressure, while each change in the operating pres- 4.411s connected.

sure necessarily has some eifect upon the position of the parts of thereset mechanism. Ultimately, and, in fact, fairly rapidly, the bars land IE will reach positions example, the positions ll indicated inFigure 4.

By comparing Figure 2 with Figure 4, it will be noted that bars I5 andIS in Figure 2 occupied positions for a IOU-pound flow, whereas in ofequilibrium as, for

Figure 4, they occupy positions #11 for the same flow. In other words,the reset mechanism has reset itself from one position for one flow toanother position for the. same flow, and, in doing so, has reset thenozzle l3 of the air-leakage relay R from one value of air leakage(position #10 in Figure 2) to another value of air leakage (position #11in Figure 4).

It will be understood that the operation of the various parts of thecontrol mechanism is instituted more or less simultaneously but occursat the different rates occasioned in part at least, by the capillarycoils 24 and 29. It will also be understood that the air leakagerelayRwill operate, in response to an increase in the weakliquor flow, todecrease the operating air pressure, and that t he reset mechanismM willoperate, in response tda decrease in the operating pressure, toreset-the air relay R to the smaller value of air leakage necessary tomaintain the smaller operating air pressure.

The foregoing control system' operates as a straight flow control, thatis to say,'it operates to maintain the flow at a given value. Aspreviously pointed out, link 2| has heretofore beenlongitudinallyshifted manually to readjust the control system from'onecontrol point to another to accommodate changes in an operatingcondition of the absorption system requiring for correction a new rateof weak-liquor flow. Changes in either the capacity of the absorptionsystem or in its operating ratio are changes of this character. Now ithas been assumed that the reset mechanism has been set at a controlpoint corresponding to a"100-pound flow. It changed operating conditionsrequire a larger or smaller flow, then link 2| should be shifted in onedirection or another to reset the mechanism to the appropriate controlpoint. In accordance with my invention, this readjustment is occasionedautomatically by means of an auxiliary control system P substantiallyidentical to the control system F. The operation of the auxiliarycontrol system P is instituted through a suitable indicator responsiveto changes in some'condition of pressure or temperature in theabsorption system which conditions should be maintained constant. Forexample, it maybe responsive to changes in the refrigerating temperatureof one unit. or another. Preferably, however, it is made responsive tochanges in the gas Pressure of the gas line 3. The shift in the link 2|is effected by connecting the terminal'pressure line of the auxiliarycontrol system Pin a bellows to which link Silhgthe auxiliary control Pis substantially identical to the control F, it is not described in vrections necessitated by detail, but its parts are designated by numbersten times higher than the numbers given to the corresponding parts ofcontrol It should suflice, therefore, to say that a pressure gauge 80 isused to operate a control arm Ill in response to changes in the gaspressure of line 3. This control arm I00 H0, to flapper I20 in the usualway. The terminal pressure line 280 is connected to a pressureresponsive bellows it which, in turn, is conis connected, throughlinkage 'sufilcient to permit control F to changes in the weak-liquorflow,

nected directly to the readjusting link 2| of control F. The bell crank200 may be adjusted to a predetermined position, corresponding to thegas pressure to be maintained constant in line 3, by means of a handcontrol H which is connected through link 2M to link ISM. The only otherdifference between the auxiliary controls F and P is that the capillarycoil 290 of control P is designed to provide an operating lag in.control P similar to the lag in the refrigerant cycle while thecorresponding coil as of control F is designed to provide this controlwith an operating lag similar to the lag of the liquor cycle. The lagproduced'in the operation of control P is correct unnecessary orundesirable changes of minor character in the flow of weak liquor andthereby substan-' tially restrict the operation of control P tocorchanges in the flow of weak liquor occasioned by changes in operatingcondition. I

It will thus be evident that variations in the weak-liquor flow wouldcause variations in the gas pressure, but, due to the lag in therefrigerant cycle, the corrections in the weak-liquor flow will beoccasioned by control F largely before control P can institute andcomplete a correcting operation; However, when the load of therefrigerating system is changed, or when operating conditions, such ascooling water temperature or available steam pressure changessufficiently to require a different weak liquor flow for the same gaspressure, the control F will attempt to maintain the same weak-liquorflow for which it is set, but this will result in a change in gaspressure. Accordingly, as the gas pressure begins to rise or'fall, thecontrol P will be operated to effect the ting of control F, and therebyincrease ordecrease the flow of weak liquor to a new value which the newcondition requires. If the change be accomplished rapidly, thecorrection will be accomplished rapidly as a result of the rapidoperation of the fast-acting bellows I40. On the other hand, if thechange occurs gradually, the correction will occur more or lesscontinuously in a gradual manner because the time interval of the changeP rmits the slow-acting bellows I10 to operate but slightly behind theoperation of the fast-acting bellows I40. From this, it should 1 beeffected either rapidly or slowly in response to rapid or ditions.

Having described my invention, I claim:

slow changes in the operating con- 1. In a control system forpneumatically con-' trgl li ng,the,we ak-liquor valve in an absorptionrefrigerating system of the closed cycle type whereinweak-liquor from aheat exchanger and gas from an evaporator are both fed to an absorber toform a strong liquor, the combinationcontrol system of the reset having:a terminal pressure line charged with with a mam?! an operatingairpressure and connected pneumatically to the weak-liquor valve toadjust the latter in response to changes in its operating air pressure;an air leakage rela responsive to to change the move the valve a resetmechanism,

operating air pressure in order to and thus restore the flow;

necessary readjustment of the setthe flow is restored the relay will airpressure at responsive to changes in the Operating air pressure, toreset the air-leakage relay so that when maintain the the changed value;and a conthe reset mechanism and the air leakage relay which connecti isadjustable to difierent control points corres ding to differentweak-liquor flowsoi an auxiliary" control system of the same reset type,responsive to changes in an operating condition of the absorption systemrequiring for correction a new rate or weak liquor flow, for adjustingthe control point connection of the main control system to the new flowrate, the auxiliary control system having: its air leakage relayoperating, in response to changes in said operating condition, to changeits operating air pressure; its terminal pressure line connectedpneumatically to the main control point connection and operatin inresponse to changes in its operating air pressure, to adjust the maincontrol point connection; and its reset mechanism operating, in responseto changes in its operating .air pressure, to reset the air leakagerelay so that when said other operating condition is corrected, therelay w i,ll maintain the operating air pressure at the changed value. pa

2. The combination defined in claim 1 wherein the air leakage relay ofthe auxiliary system operates in response to changes in the absorber gaspressure.

3. An automatic control system for penumatically controlling the weakliquor'valve in an absorption refrigerating system of theclosed cycletype wherein weak-liquor from a heat exchanger and gas from anevaporator are both fed to an absorber to form a strong liquorcomprising: a

nection between ating air pressure,

- in the air leakage relay of the main control system of the resettype-having: a terminal pressure line charged with an operating airpressure and connected pneumatically to the, weak-liquor valve to adjustthe latter in re sponse to changes in its operating air pressure; an airleakage relay, responsive to changes in the weak-liquor flow, to changethe operating air pressure of said line in order to move the valve andthusrestore the flow; a reset mechanism, responsive to changes in theoperating air pressure to reset the air leakage relay so thatxvghen theflow is restored, the relay will maintain the air pressure at thechanged value; and a connection between the reset mechanism and the airleakage relay which connection is adjustable to different controlpoints'corresponding to difierent weak liquor flows; and an auxiliary"control-system of the same reset type-having: a terminal linechargedwith an operating air pressure and connected pneumatically to the maincontrol point connection to adjust the latter in response to changes inthe operating air pressure or the auxiliary system; anair leakage relay,responsive to changes in an operating condition of the absorption systemrequiring-for correction a new rate of weak-liquor flow, to change t eauxiliary operat-' ing air pressure; and a reset mechanism operating, inresponse to changes in the auxiliary operto reset the air leakage relayso that when .said operating condition is corrected the relay willmaintain the operating air pressure to the changed value.

4. The control system defined in claim 3 whereauxiliary system operatesin response tochanges in the absorber gas pressure.

" FRANCIS P. SHANNON.

